[SQLite] add table to persist decrypted messages

Summary:
Schema:

• id: this is a field working as autoincrement, in queries we'll pass it as NULL, and SQLite engine will automatically assign it to track messages order (docs)
• message_id: message ID needed to later confirm to the other peer that the message was processed/backed up
• sender_device_id: messages sender
• plaintext: decrypted messages
• status: messages status to distinguish in what phase this message is, it will be something like received | processed | backup-done

Test Plan:

1. Migration
2. Creating DB from scratch

Reviewers: tomek, marcin

Reviewed By: marcin

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11722